I. Field of the Invention
The present invention is generally directed to a method and apparatus for voltage upconverting. More particularly, the present invention is directed to a method and apparatus for providing a miniaturized, flexible high voltage up-converter. Aspects of the invention are particularly useful in providing an apparatus comprising a plurality of up-converting modules while also allowing the apparatus to maintain a desired degree of flexibility. However, certain aspects of the invention may be equally applicable in other scenarios as well.
II. Description of Related Technology
In conventional angioplasty operations, a stent is inserted into a patient's artery that may be occluded or constricted by plaque. These stents allow a surgeon to, via in-vivo stent manipulation and guidance, enter the patient's body and keep the occlusion unrestricted. If, subsequently, the stent occluded again, irradiation of the constricted stent area may be required. Alternatively, catheters may be used to irradiate a cancerous growth. Irradiation occurs with radioactive seeds emitting beta or gamma rays. To produce these beta or gamma rays, however, the catheters have to be provided with means allowing those radioactive seeds to travel to the site where treatment is needed. These seeds are highly radioactive and irradiate the entire length of the artery from insertion point to the treatment site. Once removed from the shielding container, they pose a health risk to the patient and the medical professionals administering treatment. To solve some of these problems associated with the radioactive seeds, it is desirable to provide an X-ray generating device that generates an X-ray source near the desired area and the X-ray dose can be generated in-vivo at will. Because the radiation must be produced at the site of interest (i.e., at the obstructed artery or the cancerous growth), this X-ray tube is typically located at a distal end of the stent or catheter.
Under ordinary operation, these X-ray tubes require a high degree of power (voltage) to operate. For example, U.S. Pat. No. 5,090,043 entitled “X-ray Micro-Tube and Method of Use in Radiation Oncology” to Parker et al. teaches the use of an apparatus and method for the treatment of a patient having a tumor.
Parker et al. teaches using an X-ray generating source positioned at a location in close proximity to site or application (e.g., an artery, a vein, or a tumor). The X-ray generating source is operable at a voltage level in the range of approximately 10-60 kilo-electron volts (keV) to thereby enhance absorption of the generated X-rays by the tumor and minimizing the side effects of radiation therapy on the patient normal tissue.
Therefore, to provide the necessary voltage and power to certain types of miniature X-ray tubes, approximately 10-60 keV are required. For treatment of occluded stents, approximately 20 kV are sufficient. To provide this high level of voltage at a distal end of a catheter, the power must be provided along the entire catheter cable to the catheter distal end. Proposed catheters, however, are provided with a lengthy high voltage power cable. For example, a proposed catheter high voltage cable is typically on the order of three feet in length. Therefore, a dangerous situation arises where the peak voltage of 20 kV must traverse along the entire length of the catheter cable and then along the length of the catheter to eventually reach the X-ray unit.
Providing this peak voltage along a high voltage cable feeding the catheter and then also running the entire length of the catheter poses certain dangerous operating conditions. For example, storing such a large amount of energy can accidentally and/or inadvertently discharge and harm or fatally injure a patient and/or physician. Flashover between the high voltage components and an exterior housing of the catheter (an electrical ground) could harm or even kill the patient, the administering physician, and/or others involved in the in-vivo operation (e.g., members of the operating staff). Flashover occurs where there is leakage between the outside grounded and the inside high-voltage and this leakage if followed by a dielectric breakdown. This flashover concern exists along the entire cable length.
Therefore, because of a requirement for a long high voltage cable, most proposed miniature X-ray tube catheter systems behave as essentially a very large, charged capacitor.
There is, therefore, a general need to be able to reduce the necessity of a lengthy high voltage cable. There is also a general need to reduce a high voltage system's overall capacitance, and therefore potential flashover. These general needs should also be met while also being able to generate a high enough voltage for X-ray application at the point of observation or X-ray application.
Aside from these high voltage breakdown and capacitance concerns, there is also a maneuvering or manipulating concern associated with catheters containing miniaturized X-ray tubes. For example, because such medical devices may be used in a variety of applications (e.g., angioplasty, tumor irradiation, etc.), the catheter containing certain components must be flexible enough so that during an in-vivo operation, a user of the device (i.e., a surgeon) can maneuver and/or manipulate the subject catheter so as to manipulate or guide the X-ray unit along an artery to accurately position the catheter at a desired location. Because certain proposed miniature X-ray tubes have been large (larger than 2.5 mm in diameter), there is a further need for a flexible, guidable device comprising a X-ray tube device having a diameter less than 2.5 mm. It is believed that an ideal X-ray tube for angioplasty procedures has a diameter ranging from 0.5 to 1.0 mm. Other diameter sizes could also be desired depending on the application of the X-ray tube.
Even though the same proposed concepts may describe a relatively compact voltage source, the dimensions of such voltage sources are large, often on the scale of inches. For example, the voltage source disclosed in U.S. Pat. No. 4,241,360 discloses a voltage source having a size on the order of 0.5 inches in length (12 mm) and 0.2 inches wide (5 mm). For medical applications, and especially for catheters that are inserted inside a body, further miniaturization is desired. In addition, where a voltage source is used in a catheter or other in-vivo applications, the catheter and hence the voltage source must have some degree of flexibility and maneuverability.
There is also a need to provide a miniaturized power source that reduces the risk to the patient by minimizing the discharge power and while also maintaining catheter flexibility. There is also a general need to provide a power source that can be guidable through difficult passageways and provide a source of power at difficult to reach areas.